Microfluidic devices are increasingly used to perform biological experiments on a single-cell basis. However, long-term stability of cell positions is still an issue. A novel biocompatible method for cell entrapment and release on a microchip is presented. It is based on the controlled formation of an alginate hydrogel by bringing two laminar flows of alginate and calcium ions in the range of 2 mM to 40 mM into contact. The resulting growth of a gel bar is used to enclose and immobilize yeast cells. Adding ethylenediaminetetraacetic acid (EDTA) to the alginate solution allows for control of the hydrogel growth, and by varying the ratio of Ca(2+) to EDTA concentrations gel growth or gel shrinkage can be induced at will. Trapped cells are released during shrinkage of the gel. The trapping efficiency for different cell speeds is investigated and the properties of gel growth are discussed using a diffusion model. Precise positioning of a single cell is demonstrated. The technique presented allows not only the reversible immobilization of cells under gentle conditions but also offers the potential of long-term cell cultures as shown by on-chip incubation of yeast cells. The procedure may provide a simple and fully biocompatible technique for a multitude of innovative experiments on cells in microsystems.

In this work we present the formation of micrometre-sized lipid vesicles and tubes with perfectly homogeneous diameter and extraordinary length. The method is a novel approach for unconventional fabrication of soft-matter microstructured devices based on the combination of top-down and bottom-up fabrication processes. Photolithography techniques are applied to fabricate microsized apertures that provide the requirements to form lipid structures with predictable size and to align and guide the vesicles and tubes in microstructured channels. The formation is facilitated by self-assembly of polar lipids to a lipid membrane that is afterwards forced to undergo a shape transformation by extrusion through a microsized aperture. Both the geometrical restriction by the small aperture and the pressure difference between the top and bottom sides of the aperture determine the form and length of the vesicles and tubes. A strong pressure difference favors the formation of lipid tubes, while a low pressure difference results in the formation of vesicle bunches with spherical and cylindrical shapes. Potential applications for the formed lipid structures could be as microreactors and transport channels as well as in the construction of flexible microfluidic networks.

Processing techniques are reviewed that allow the introduction of ceramic components made from powders into microelectromechanical systems (MEMS). Ceramics have several advantages over other materials also in microsystems, e.g., heat resistance, hardness, corrosion resistivity, or functional properties. The range of available materials in microfabrication technology is being increased beyond those deposited by thin‐film technology. Top–down approaches like mechanical and laser‐based direct writing processes, ink‐jet printing, microextrusion, and lithography‐based methods are presented. They are complemented by some more fundamental work in the field of bottom–up synthesis of micro‐ and nanoscaled ceramic materials.

With the introduction of soft lithography and micromolding in capillaries, low‐cost microfabrication with liquid materials has become possible. In this article, we demonstrate how to fabricate porous ceramic lines of 10 μm width and several millimeter length on silicon wafer substrates by using colloidal suspensions of tin oxide. Microchannels of poly(dimethylsiloxane) (PDMS) served as molds that were spontaneously filled owing to capillary forces with suspensions of 0.1–40 vol% solid loading. The resulting ceramic lines have a height of about 7 μm and therefore differ from the usual ceramic thin film coatings. The capillary filling characteristics were observed under the microscope, and the implications of rheology and suspension chemistry are discussed and evaluated. Using the same capillaries, even smaller lines (2–3 μm width) of powder particles could easily be prepared by adjusting only the solid content of the suspensions.

α-Cyclodextrin, α-CD, which does not adsorb on mica, can be bound to this surface as a polymeric inclusion compound that is formed by threading many α-CD rings on a cationic polyelectrolyte, poly(decamethylenebipyridinium dibromide). The major driving force of the adsorption of the polymer and the polymeric inclusion compound is ion exchange with surface ions of mica. Somewhat less polymer is adsorbed when it is engaged in the inclusion complex than as pure polymer. The rates of adsorption for both the polymer alone and for the polymer in the inclusion compound depend strongly on the particular cation initially present at the mica surface (Li+ or K+); it is much more rapid with Li+. The equilibrium between complexed α-CD and uncomplexed α-CD, found in solution, is modified upon adsorption of the complex to favor the release of α-CD from the complex. However, the α-CD is only slowly released from the complex on the surface and, as a result, mica-bound complex can be isolated.